One of the major requirements of smoke stacks is the requirement to remove sulfur dioxide (SO.sub.2) gas from the combustion gas stream. This is generally accomplished by spraying a lime solution into the gas stream. As the small droplets of lime solution come into contact with the sulfur dioxide in the gas stream, the calcium in the lime solution reacts with the gas sulfur dioxide to form calcium (CsSO.sub.4) and calcium sulfate (CASO.sub.3) which are solids that can be removed by dust collectors. There is also unreacted lime (CaO) which is removed by the dust collectors along with the combustion fly ash.
Before the sulfur dioxide scrubbers were installed, the fly ash could be conditioned with a water addition in a paddle or drum mixer. While these units did a marginal job, it was acceptable and low in cost. With the ash from sulfur dioxide scrubbers, the lime, calcium sulfide and calcium sulfate together with the fly ash all of which are very fine particles make the blend of materials act like a pozzuolanic or portland cement. When water is added in a paddle mixer, the fly ash begins to set and hardens so that the paddles are constantly wearing against the hardened cement liner and causing breakdowns.